The present invention relates to a semiconductor device, and more specifically to a fuse structure of a semiconductor memory device, as well as a method of manufacturing the same, that is, in short to improvement of the fuse structure of a semiconductor memory device.
Recently, in the field of semiconductor integrated circuits, the degree of the high integration further advances, and in particular, in DRAMs, a high integration density of a level of giga bit is required. Further, due to the characteristics of the memory element of the semiconductor memory device, a large-scale redundancy circuit must be inevitably provided. Therefore, the integration density of the semiconductor integrated circuit is further increased. For this reason, it is becoming essential to decrease the area of a fuse element in order to reduce the element area.
A fuse region of a conventional DRAM will now be described with reference to FIGS. 17A and 17B. Here, FIG. 17A is a cross sectional view of the fuse element, whereas FIG. 17B is a top view of the fuse element. A cross section taken along the line XVIIAxe2x80x94XVIIA in FIG. 17B is indicated as FIG. 17A. As can be seen in FIG. 17A, an element separation region 101 is formed in a surface region of a semiconductor substrate 100. On the element separation region 101, an interlayer insulating film 102 having a thickness of about 1.4 xcexcm, which is made of a silicon oxide film or the like. A plurality of metal fuses 103 having a thickness of 2000 to 3000 angstroms, which are made of aluminum or the like, are formed on the interlayer insulating film 102 so as to be adjacent and parallel to each other.
In the structure shown in FIG. 17B, as a laser beam is applied to a fuse portion 104 which is a fusing (meltdown) region, the portion breaks down in a manner of joule breakdown by heat, and fuses. It should be noted here that the length of the fusing region 104 of each one of the fuses 103 is about 1.0 xcexcm, and the width (that is, taken in a direction normal to the direction of the length) of the fuses in a region other than the fusing region 104 is about 0.6 xcexcm. On the fuses 103, an interlayer insulating film 105 having a thickness of about 500 to 5000 angstrom is formed to cover the fuses 103. Please also note that in a fuse region of the prior art technique, a special process step is provided to form a fuse opening section, and a film corresponding to the interlayer insulating film 105 is formed to have a certain thickness on a metal fuse 104.
However, the conventional semiconductor as described above entails the following drawbacks.
That is, in the fuse structure of the conventional technique described above, the interval between fuses is narrowed as the element is downsized. With this structure, when broken pieces of a fuse are scattered from a melted-down fuse and stuck on some other fuse which should not be melted down, the erroneous meltdown of that fuse which should not be melted down, or the change in the resistance of the fuse (or the corresponding circuit) are induced, creating a problem that a desired element operation cannot be guaranteed. Further, as the wire is multi-layered, the thickness of the film cannot be made uniform any more from one site to another in the interlayer insulating film. Therefore, when a plurality of fuses are provided, the thickness of the portion of the insulation film, which is located on each fuse differs from one portion to another. As a result, when a laser beam is applied uniformly onto a plurality of fuses, insufficient meltdown or excessive meltdown may occur. Further, in the case where the interlayer insulating film formed underneath fuses is multi-layered, the stress of a fuse which is scattered into pieces while the meltdown of the fuse is easily propagated between insulating films made of different compositions, and therefore in some cases, a fuse which should not be melted down is melted due to the propagated stress. In order to prevent such a phenomenon, the energy level of the laser is limited to a low level such as about 0.9 xcexcJ, and such a limited energy level is in some cases insufficient to surely melt down a desired fuse depending on a situation determined by, for example, the thickness of the insulating film on a fuse.
As described above, with the conventional semiconductor device, in order to melt down a very fine fuse, heat is applied to the fuse through an insulating film. Therefore, a meltdown error of fuse caused by the non-uniformity of the thickness of the insulating film, or other type of meltdown error caused by the propagation of the stress when a fuse is scattered in meltdown, due to the difference in the material of the underlying insulating film, occurs. For example, in the case of a silicon oxide film having a multi-layer insulating film structure, as shown in FIG. 18, with its underlying layer being a TEOS film (tetraethyl ortho silicate) 106 and its overlying layer being an HDP (high density plasma) film 107, as laser energy is irradiated on a melted-down fuse 108, a stress created as the melted-down fuse scatters is propagated between the TEOS film 106 and the HDP film 107 as indicated by an arrow in FIG. 18, thereby causing an adverse effect on an adjacent non-melted fuse 109. Thus, in some cases, the fuse which should not be melted down is wrongly fused depending on a situation. Further, even if it is not fused, the width of wiring of the fuse which should not be melted down, is narrowed due to the adverse effect of the stress caused by the scattering of the fuse, thus increasing its resistance value.
An object of the present invention are to solve the above-described drawback of the prior art technique. More specifically, the object of the invention is to provide a fuse element capable of fusing a very fine fuse uniformly without being influenced by the thickness of the insulating film on the fuse, as well as a method of manufacturing such a fuse element.
Another object of the present invention is to provide a highly integrated fuse element in which an adverse effect on an adjacent fuse element is suppressed by reducing the amount of scattering pieces of a meltdown fuse when it is fused.
In order to achieve the above-described object, there is provided, according to a first aspect of the present invention, a semiconductor device comprising a semiconductor substrate; a first insulating film region provided in a groove-like manner in the semiconductor substrate; a fuse element provided on the first insulating film region; a second insulating film region formed on the fuse element and the first insulating film region; and a metal plug connected to the fuse element, and having a surface exposed to a surface of the second insulating film region.
In the semiconductor device according to the first aspect of the present invention, the metal plug may include a portion projecting on the surface of the second insulating film.
There is further provided, according to a second aspect of the present invention, a semiconductor device comprising a semiconductor substrate; a first insulating film provided on the semiconductor substrate; a first fuse element provided on the first insulating film; a second insulating film formed on the fuse element and the first insulating film, the second insulating film having a via hole formed therein; and a first metal plug formed in the via hole formed in the second insulating film, the metal plug being connected to the fuse element, and having a surface exposed to a surface of the second insulating film.
In the semiconductor device according to the second aspect of the present invention, the surface of the first metal plug may be depressed in the via-hole is removed.
In the semiconductor device according to the second aspect of the present invention, the first metal plug may have a portion projecting on the surface of the second insulating film.
In the semiconductor device according to the second aspect of the present invention, the semiconductor device may further comprise an element separation film formed on the semiconductor substrate, wherein the via hole formed in the second insulating film may be above the element separation film, and the first metal plug may be above the element separation film. The surface of the first metal plug may be depressed in the via-hole is removed. The first metal plug may have a portion projecting on the surface of the second insulating film.
In the semiconductor device according to the second aspect of the present invention, the semiconductor device may further comprise an element separation film formed on the semiconductor substrate, wherein the first insulating film may have an open hole formed therein, a second metal plug may be provided in the open hole formed in the first insulating film, the open hole formed in the first insulating film may be outside of a region of the element insulating film, the via hole formed in the second insulating film may be outside of the region of the element separation film, and the first metal plug formed in the vial hole of the second insulating film may be outside of the region of the element separation film. The surface of the first metal plug may be depressed in the via-hole may be removed. The first metal plug may have a portion projecting on the surface of the second insulating film.
In the semiconductor device according to the second aspect of the present invention, the semiconductor device may further comprise an element separation film formed on the semiconductor substrate, a second fuse element formed on the first insulating film, and a third insulating film provided between the first insulating film and the first fuse element, the third insulating film having an open hole formed therein, a second metal plug provided in the opening hole formed in the third insulating film, wherein the open hole formed in the third insulating film may be above the element insulating film, the second metal plug provided in the opening hole may be above the element insulating film, the via hole formed in the second insulating film may be above the element separation film, and the first metal plug formed in the vial hole of the second insulating film may be above the element separation film. The surface of the first metal plug may be depressed in the via-hole may be removed. The first metal plug may have a portion projecting on the surface of the second insulating film.
With the above-described structures, it becomes possible to carry out meltdown of a fuse without having a non-uniform meltdown of the fuse or erroneous fusing caused by the stress created in the scattering of a melted-down fuse due to the difference in the material of the underlying insulting film. Therefore, with the present invention, a fuse element capable of uniformly melting down a very fine fuse without adversely affected depending on the thickness of the insulating film on the fuse, can be provided.
Further, according to a third aspect of the present invention, there is provided a method of manufacturing a semiconductor device including the steps of: forming an element separation region on a semiconductor substrate; forming a first insulating film on the element separation region; depositing a metal fuse on the first insulating film; depositing a second insulating film on the metal fuse; removing a region of the second insulating film, where a via-hole is to be formed, by etching; depositing a metal film on the second insulating film such as to completely embed the via-hole formation scheduled region; and forming a metal plug by etching a section of the metal film, other than a region where a plug is to be formed. With this structure, a metal plug can be formed on a fuse while reducing the number of processing steps, and further it becomes possible to prepare a fuse of a high controllability, which is not affected by the thickness of the insulating film on the fuse.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.